This invention relates to protecting a splice in multi-wire electrical cables, in particular communications cables, from ingress of water into the splice.
Multi-wire electrical cables comprise a core containing a plurality of individual insulated wire conductors, surrounded by an outer sheath. The cable core can contain from a few pairs of conductors up to several thousand pairs. The outer sheath generally consists of an outer plastic jacket surrounding a metallic shield. Additional inner polymeric layer or layers can be present. To protect the conductors from water, the interstices between the individual wire conductors can be filled with a filling compound, usually a grease based or petroleum jelly. Cables that are so filled are generally referred to as "filled" cables and cables that are not filled are generally referred to as "air core" cables. Air core cables can be pressurized to prevent ingress of water.
When a splice is made in a cable, the outer sheath is removed from the end of the cable. At least some of the individual wire conductors in the core of the cable are joined to conductors of another cable or cables. After completion of the splice, the entire splice area, that is the area of the cables where the sheath has been removed, must be protected. Generally, an enclosure or splice case is placed over the area. A preferred enclosure is a dimensionally recoverable polymeric sleeve, preferably a heat-shrinkable polymeric sleeve. An inner protective casing or lining can be positioned about the splice before installation of the sleeve to provide additional mechanical protection. Molded plastic or lead splice cases are also used.
The splice case can be filled with a suitable filling compound to protect the individual wire conductors in the core of the splice (referred to herein as the splice bundle or splice core). Such filling compounds can be curable liquid polymer systems or grease-like materials, generally based on petroleum jelly. Curable liquid polymer systems are used by pouring a curable liquid sealant into a splice case positioned about the splice and allowing it to cure. Particularly useful curable liquid sealants are two-part polyurethane systems comprising a prepolymer and a curing agent or hardener. When cured the filling compound solidifies, preferably to a gel-like consistency, forming a protective layer around the splice. It has been found that this technique doesn't adequately protect the splice from ingress of water, particularly if one of the cables contain 400 pairs or more of wire conductors. Seepage of water into the splice eventually causes electrical failure of the joined conductors.